The present invention relates generally to apparatus for feeding objects into and unloading objects from a punch press, and relates more particularly to a high-speed automatic apparatus for downsetting die pads of lead frame strips.
Integrated circuits are commonly packaged inside a protective enclosure by mounting the chip containing the circuits on a lead frame located within the enclosure. The lead frame provides electrical connections between the chip and the outside of the enclosure. Typically, a lead frame is fabricated from a thin sheet of metal and has a die pad for mounting the chip and several electrical conductors surrounding and fanning out from the die pad area. Lead frames are commonly fabricated in strip form with several lead frames joined together. Some lead frames are fabricated in very long strips which are wound onto reels, others are fabricated in short strips containing approximately ten lead frames.
A lead frame is a flat piece of metal which is stamped or etched to remove portions thereof to define the die pad and the conductors. It is desireable to downset or lower the die pad by a distance equal to the thickness of the chip to be mounted to facilitate the subsequent process of wire bonding for electrically connecting the contact pads of the chip to the conductors of the lead frame. The process of wire bonding is performed with the aid of microscope viewers to allow an operator to guide a wire feed mechanism between the contact pads and the surrounding conductors. Downsetting enables the contact pads to be at the same elevation as the conductors, thereby eliminating refocusing of the microscope viewers and simplifing the movement of the wire feed mechanism.
The prior art technique for downsetting short strips of lead frames has been a manual operation where an operator sequentially places and positions a lead frame strip into a die set in a punch press, actuates the punch press, and removes the downset lead frame strip. One drawback to this manual technique is that productivity is low because of the high labor content and slow production rate. Potential for serious operator injuries is another drawback to this manual technique.
It would be desireable, therefore, to provide an apparatus for automatically loading lead frame strips into a die set, downsetting the lead frame strips, and unloading the downset lead frame strips. It would also be desireable for such an apparatus to be high-speed so as to minimize the unit cost of downsetting lead frame strips. Additionally, it would be advantageous for such an apparatus to be easily converted to accomodate a variety of lead frame strip sizes. The automatic apparatus of the present invention provides these advantages.